This invention relates to an apparatus for manufacturing a glass stem, and more particularly to a universal lower stem mold capable of making a cathode-ray tube (CRT) glass stem having from five to twelve lead-in conductors (or leads) extending through a glass disk in a direction perpendicular to the plane of the disk and forming a circular array of leads.
U.S. Pat. No. 3,201,216 issued to Handmann on Aug. 17, 1965 describes an apparatus for producing an electronic tube stem. Such a stem is usually made by inserting the leads in openings in a rotatable lower portion of a stem mold which is mounted on an indexable turret. A glass cylinder is placed on the lower stem mold assembly around or within the leads (or both) and then the leads and the glass cylinder are heated to melt the glass. The glass cylinder is pressed into a disk in which the leads are embedded. Each of these operations takes place at an indexed position of the turret. During the heating operation, the leads, the glass cylinder, and the lower portion of the stem mold assembly, are rotated to uniformly heat the glass. During the pressing step, the upper portion of the stem mold assembly is pressed down onto the glass cylinder. Usually, the upper mold assembly is either rotated in synchronism with, and in properly indexed relation to, the lower mold assembly, or the lower mold assembly is stopped in properly indexed position relative to the stationary upper mold assembly. When the upper mold assembly is lowered to the pressing position, the leads extend into lead receiving holes in the upper mold assembly. As is known in the art, a tubulation is usually centrally disposed within the disk to permit evacuation and seal-off of the CRT. While most rotary stem machines have 24 or 30 lower stem mold assembly positions, there usually are only two, three or four upper mold assembly positions on a stem machine, the actual number reflects the preference of the machine designer. While the upper mold assemblies differ slightly from station-to-station and can be though of, for convenience, as progressing from a rough press to a finished press, the lower stem mold assemblies, which transport the stem during the manufacturing operation, are identical to one another. It is the present practice to provide a specific lower stem mold for each type of CRT stem made. In other words, a five lead stem requires a lower stem mold having five lead openings therethrough to accommodate the five leads of the stem. Twenty-four or thirty such stem molds are required for each stem machine. If a nine or twelve lead stem is to be produced, each of the twenty-four or thirty lower stem molds in the stem machine must be changed to stem molds having the required number of lead openings. This change in lower stem mold configuration makes it inconvenient and expensive to change the stem design, for example to change the number or location of the stem leads. Even if a stem machine is dedicated to producing only one type of stem, occasionally it is necessary to replace a worn or damaged lower stem mold and a variety of different molds must be maintained in inventory to accommodate the different stem types.